If your looking for regular WC true percs Live aquaria usually has some. If your looking for Onxy true percs I'd get them from Rods-reef.com, his are tank bred & raised & the best looking onxy out there. If your looking for picasso true percs I'd go with bonesreef.com he's producing some awsome looking picasso's!
If your getting WC clowns I'd QT them.
Clowns eat pretty much anything, no special care required unless you get some young juvi clowns, then they will need smaller foods ... but thats about it. Percs are very easy to care for once they are healthy out of QT.